Gas tungsten arc welding, also commonly known as TIG welding, is a process that produces an arc between a non-consumable tungsten electrode and a workpiece, protected from oxidation by an inert gas shield. This welding process works especially well for relatively thin metals, such as stainless steel and aluminum, less than 0.125 inches in thickness. Although relatively slow for thicker metals, TIG welding is used for thicker welds in industries such as aircraft, aerospace, and nuclear facilities, where high quality is required. TIG welding also has an advantage over some other processes in that a welder can weld in any direction or position. A description of TIG welding and other welding procedures can be found in the Metals Handbook, published by the American Society for Metals, in volume 6 entitled "Welding, Brazing and Soldering".
As there are numerous combinations of metals, thicknesses, and joint geometries to weld, so there are numerous types of TIG welding torches and combinations of inputs to those torches required by the welder to match such combinations. See the Metals Handbook, pp 182-213, for discussion and tables relating these factors.
The torch has several important physical characteristics, particularly the size of the electrode, and its general shape and weight. For example, torches typically have electrode diameters that vary from 0.04 inches to 0.125 inches, depending on the metal, thickness, and type of weld. Depending on the electrode diameter and other factors, the nozzle around the electrode can be made from one of several materials and can be either cylindrical or tapered, certain shapes allowing the welder to use less gas. Weight of the torch typically varies from 1 ounce to 15 ounces, welders generally preferring to use as light and comfortable a torch as possible for a given job. If accessibility to a weld joint is difficult, there are torches shaped to reach various piecepart angle configurations for welding around corners or through small openings.
There are three main inputs to the torch: current, gas, and coolant. Current can be AC or DC and can range at least from 3 to 500 amps AC, depending on the torch and on the size of electrode needed. Which gas to use, for instance, argon, helium, or argon-helium is determined from the base metal composition, thickness, tungsten diameter and shape, weld joint geometry, and penetration required. These factors, in turn, determine the rate of gas flow. Coolant for the torch can be a fluid such as water or a water/anti-freeze mix. Smaller torches can be air-cooled. When using water as coolant, the water can enter the torch through its own line, either from a water circulator or from an output in the welding machine, and return through the power cable or the water can enter with the power line and return to the coolant source through a return water line. In some installations, water coolant is not recirculated, the torch being cooled from a conventional water tap outlet whereupon the water is discarded. Generally, a water type coolant is required for larger currents, thus making the torch assemblies heavier, bulkier, and less manipulative.
Welders should use a best torch configuration for a given weld-type or requirement and a variety of such weld requirements may be encountered for a given workpiece. Thus, not only is an overall weld procedure improved by using multiple torch configurations, but also costs associated with rework and rejection rates are reduced. Problems can occur when a welder attempts to save time by using only one torch for welds of different metals and thicknesses. The correct torch for a thicker metal may burn through a thinner workpiece. Conversely, the correct torch for a thinner metal workpiece may not completely penetrate the base metal while creating an appearance that the weld is sound. Welders, however, tend to start with one tool and continue to use it as long as it can somewhat perform a given job, inasmuch as switching torches is a time consuming and annoying process.
To switch torches, a welder must independently disconnect the current, the gas, and the coolant, since each line is built into the torch head. The power cable, which often includes the water suppy or water return, must be disconnected from the power block that is attached to the power supply. Usually this results in coolant spilling on the work region floor and creating a potential shock or slip hazard to the welder who may end up standing in a puddle near a power source that could accidentally be activated. If water coolant is used, the input must be disconnected either from the welding machine if city water is used, or from the water circulator. The gas line must also be disconnected from its source. Various tools are required to carryout this switch-over because the several connections are threaded, some left-handed and some right-handed. A variety of tools are called for since connections can have different adapters. The welder has to wrap the torch and the cables for storage, then obtain another torch and reconnect the various inputs and return conduits and cables. This process can often take 15 to 20 minutes. It is understandable then, that during a welding project, welders prefer to use the singular torch in their hand than to use a more properly sized and configured torch.